Long-term factors influencing the adhesion of metallized zinc to concrete

Publisher’s version / Version de l'éditeur:

Journal of Thermal Spray Technology, 5, 1, pp. 49-52, 1996-03-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Long-term factors influencing the adhesion of metallized zinc to

concrete

Brousseau, R. J.; Arnott, M. R.; Baldock, B.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=38c46b62-4ccb-4237-a8e7-01f95fe0e84d

https://publications-cnrc.canada.ca/fra/voir/objet/?id=38c46b62-4ccb-4237-a8e7-01f95fe0e84d

http://www.nrc-cnrc.gc.ca/irc

Long-t e rm fa c t ors influe nc ing t he a dhe sion of m e t a llize d zinc t o

c onc re t e

N R C C - 3 8 7 8 5

B r o u s s e a u , R . J . ; A r n o t t , M . R . ; B a l d o c k , B .

M a r c h 1 9 9 6

A version of this document is published in / Une version de ce document se trouve dans:

Journal of Thermal Spray Technology, 5, (1), pp. 49-52, March 01, 1996

The material in this document is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without written permission. For more information visit http://laws.justice.gc.ca/en/showtdm/cs/C-42

Les renseignements dans ce document sont protégés par la Loi sur le droit d'auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d'identifier la source de l'information et, dans certains cas, d'interdire la copie de documents sans permission écrite. Pour obtenir de plus amples renseignements : http://lois.justice.gc.ca/fr/showtdm/cs/C-42

jTTEE55:49-52

©ASM Inlernational

Long-Term Factors Influencing the Adhesion

of Metallized Zinc to Concrete

R. Brousseau,M.Arnott, and B. Baldock

Metallized zinc cathodic protection often is used to mitigate steel reinfort::ement corrosion in concrete. The zinc is flame or8rc sprayed to the surface of the concrete structure to be protected. The metallized coating should be applied such that its adhesion to concrete is maximized. FaclOl·s believed to affect｡､ｾ

hesion were investigated for pure zinc and aＸｓｚｮｾＱＵａｬ alloy. On reinforced concrete samples polarized for more than 800 days at three different current densities, adhesion decreased. The reduction incrcuscd as afunction of time and of the current density applied. When no current was applied, there was a small

initial Increase of adhesion with time. For the metallized samples that were freeze-thaw cycled, no loss of

adhesion was fonnd afler 70 cycles.

1.

Introduction

CORROSION of reinforcing steel in concrete due to chloride

attack is a serious problem in northern climate regions and on coastal structures. Cathodic protection often is llsed toｭｩｴｩｾ

gatesteel reinforcement corrosion. It involves negatively po-larizing the steel reinforcement in order to promote chloride ion migration away from the reinforcement and to reduce the rate of anodic oxidation ofiron. This technique is usually

ap-plied

10

older and chloride-contaminated structures

experi-encing corrosion-related damage.

It

requires the application

of an anode, such as metallized zinc, on the surface of Ihe

concrete structure to deliver the protective current to the

re-bars.

Zinc coatings have been successfully implemented as

im-pressed-current anodes in Califomia (Ref 1, 2). Oregon (ReO).

and Ontario (Ref 4, 5). The Florida Departmenl of

Transporta-tion (Ref 6) has also begun to use metallized zinc as a sacrificial

anode onmarine structures.Itis. however. still unknown how

Ihis type of anode will perform in the long term.

In order for the metallized zinc

to

perform adequately as an

anode, it must have good adhesion to the surface concrete of thc

cathodically protected structure. Steps should be taken to

opti-mize the adhesion of the zinc coating when it is thermally

sprayed on the concrele surface. Earlier work (Ref 7-10) has

shown that a number of parameters can influence the adhesion ofarc-sprayed zinc to concrete.

This paper discusses phenomena that may affect adhesion

af-ter zinc has been metallized onto concrete. The effects of anodic

polarization, time from application, and freeze-thaw cycling are

reported. A85Zn-15Alalloy was also thermally sprayed in these

experiments. However,

it

should be noted Ihal zinc-aluminum

coatings are not recommended for impressed-current cathodic

protection (Ref 11, (2).

Keywords adhesion strength. cathodic protection. current density. freeze-thaw cycling. zinc on concrete

R.Brousseau, M. Arnou, and B.Baldock,NationalResearch

Coun-cil ofCanada. Ottawa. Canada.

Journal of Thennal Spray Technology

2.

Experimental Method

2.1 Thermal Spraying

Zinc and 85Zn-15AI were arc sprayed onto concrete hlocks

using a Thermion 500eleelrical arc gun. All thermal spmy

appli-cations were performed with 3 mm wires. using 620 kP:'1 air

pressure, 26 V, 300 A, and a spray distance of 15.2 cm.

All

"uto-mated application system was used to travel the electrical. arc

gun inlhex-y planc during melallizing

10

produce" uniform 0.4

mm thick coating.

2.2 Manufacture of Concrete Samples

The concrete samples were manufactured in thrce different

configurations and sizes to meet test requirements. The concrete mix design was the samefor each of thethree tests.Thecollcrete

formulationusedacement/sand/aggregateratioof1:2:3, type

10 Portland cement, and a water

10

cement ratio of 0.43.

Chlo-rides were also introduced into the concrete mix tobetter simu-late aggressive environments. The samples were cured in a

humid room at 23'C and 100% relative humidity for 28 day•.

Unless otherwise indicated. the concrete surfaceswere blasted

wirh silica sand at 758 kPa air pressure prior to metallization

with

zinc.

2.3 Adhesion Measurements

Bond strength measurements were obtained using a pneu-matic adhesion tester referred to as a HPatti." This equipment

uses 50 mm dollies. The pulling force is perpendicular to the

sur-face of the samples aud is applied at a constant rate that is not

op-erator dependent. A thick, high-strength, slow-setting, two-part

epoxy was used to glue the dollics.

2.4 Samples under Impressed Current

The effect ofimpressed currents on metallized zinc adhesion

was investigated using 60 concrete samples reinforced with a

mild steel mesh (Fig.

I).

The metallized concrete samples were

placed in individual plastic containers partially filled with a

saturated salt solution. The lower 1.0 em of each sample was

..,.

I

ways immersed in the salt Solulion. The samples were sub-sequently wired in series and polarized at three differem current

densities-o, 2, and 10 mA/m2-per anode surface. Ten

repli-cates of each anode material were tested for each of the three

current densities.

E /.",;A ｾ

e,,,.,

I

w;"

m,,'

ｾ

ITI ') '0

I FUR&ctlfler

'...

Concrete Detail "A"

.r---

356m'"ｾ

r

_ｾ

m

L,----Fig. 1 Schematic diagram of polarized samples

2.5 Freeze-Thaw Procedure

The adhesion of zinc coatings exposed to freeze-thaw cy-cling and deicing salts was investigated via a modified version of ASTM C 672-84 ("Standard Test Method for Scaling Resis-tance of Conerele Surfaces Exposed to Deicing Chemicals"). No eurrem was applied 10 the samples. The procedure consisted

of placing the samples in a freezer (-18 ±2 'C) for 16to 18 h.

The concrete samples were subsequently removed from the freezer and thawed in the laboratory for 6 to 8 h al23 'C and 50% relative humidity. The samples were finally sprayed with a salt solution (4% by mass of anhydrous calcium chloride) before be-ing returned to the freezer for a subsequent cycle.

3. Results and Discussion

3.1 Effect

ofthe Impressed Current

After 845 days of testing, the bond strengths on all the

un-powered samples were similar to or higher than the initial bond

strength values. Values presented in Fig. 2 and 3 are averages of 3 to 15 pullout measurements. The higher bond strength for the 85Zn-15AI alloy may be due to chemical reactions between this

6000 6000

•

a. ｾ 4000

"'

'g>

"""

ｾ

'0 2000 § OJ 1000

Fig.3 Bond strength of｡ｲ｣ｾｳｰｲ｡ｹ･､ 85Zn-15Al as a function of time under an anodic impressedCllrrentdensity of 0, 2. and

to

mA/m2

-.-OmA/m2 -e-2mA/m2

ｾｉｾ

-4-10 mAlm2

I

!-*---!---t-·---a

1000 BOO

'-1-'1'-,

-m-OmNm2 -.-2mA/m2 -A-10mA/m2

"'"

4000

"""

•

a. ｾ

"""

"'

0> '500

ｾ """

-g 1500 0

'"

1000 500

""

TIme. days

Fig.2 Bond strength of arc-sprayed zinc as a function of time tinder

an anodic impressed current density ofO. 2. and lOmA/m2

"""

o ro ｾ 00 00 100

Time,Indaysfrom application

120

"""

3500

8'.

_{. " .}

'"

.c

ＭｲＫＭｾ

i

'500 /jj

ｾ """

1500 0 20 40 SO 00 100 120

Tim.,Indaysfrom application Fig.4 Time variation of theadhesion of zinc after it has been

metal-lized onto concrete.

Fig.S Time variation of the adhesion of 85Zn·15Al afterithas been metallized onto conrete

'000 ｾ Q. ｾ

"'"

.c '6>_c ｾ Iii 2000

1!

₀ tn 1000

metallized alloy and the concrete. Aluminum is known to chemi-cally rcact in higher pH environment. as a result of its am-photeric oxides. The limiting factor for many of the bond strength tests on the unpowcred samples was the tensile strength of the concrete. Failure often occurred in the concrete (cohesi ve failure).

The bond strength values for all the powered samples de-creased over the course of the experiment. Samples powered at the higher current density experienced larger decreases in bond strength. The loss of adhesion of the metallized coating under anodic polarization is believed to he related to oxidation of the "anchors" that usually provide the mechanical bonding. Molten metal that penetrated into the pores of the concrete during

met-allizing is most susceptible to oxidation during the flow of

an-odic current because these "anchors" have a more intimate

contact with the concrete pore solution through which electro-lytic current flow is forced. This also suggests that excessively large current densities at the anode will be detrimental to the ad-hesinn of the zinc coating. The 85Zn-15AI alloy should not be

used as an impressed-current anode for reinforced concrete due

to its severe loss of adhesion at 10mA/m2. An unusual

forma-tion of oil' pockets alsoOCCUI'Sunderneath the disbanding

zine-aluminum coatings. with unusual darkening. Such severe

- a - Grit blasted before aging - e -GrIt blasted aftera Ing

"""

"'"

•

_"'"

Q. ｾ

ｦｾ

t

2"" 2400 Iii 2200 '0_c 0 2000 OJ

/ '

'""

'""

-20 0 20 40 60 60 '00

_''''

'40 '60

lime in days fromapplication

Fig. 6 The effect of lime on the adhesion of arc sprayed zinc con-crete. Before itWas llrcsprayed. theCOncretewas sllbjectcd to acceler-ated aging. The concrete was grit blasted before or afterit.

-a-Zinc

ｾｯｾＬＮＢ

physical changes are not observed for pure zinc. Photographs

il-lustrating this point are presented in Ref 11.

3.2 Fffect ofRest Time after Metallization

It has been speculated, based on field observations in Oregon and Florida, that a delay in testing the adhesion of metallized zinc after application frequently resnlts in higher hond strength values. This was also noticed in the present result'. More de-tailed experiments were undertaken to study this phenomenon. The changes in bond strength overtime were monitored for both zinc and 85Zn-15AI. The surfaces of 30 concrete blocks were pretreated in three ways prior to metallizing. After metallizing,

bond strengths were monitored on all the samples that were

maintained in a 50% relative humidity atlllosphere at 22 'C.

In the first test, concrete samples manufactured as described

in the experimental procedure were metallized shortly after

completion of theircuring period, The same experiment was

re-peated twice to ensure reproducibility. Each time, no polarizing current was applied to the samples. The individual values in Fig. 4 and 5 represent averages of nine pullout tests. The results

indi-cate an initial increase in bond strengthfOfat least a few weeks

after the metallizing. The magnitude of the increase in bond strengths varies, but in some cases can be as high as 25% of the original value.

Experiments

were also conducted on aged samples to

deter-mine whether the apparent increase in bond strength was related to concrete strengthening. Concrete samples (half of which were already grit blasted) were stored for 5 months in tanks kept at 70% relative humidity and 22 'C. There was also a slight

posi-tive

overpressure

_{of CO2}to promote carbonation of the

con-crete. Thnse samples that had previously been grit blasted were metallized without additional grit blasting. All other samples

wefegrit blasted and metallized according to the usual proce-dure. Increases in zinc bond strength over time were once again

observed (Fig. 6).

Chemical interaction between the zinc coating and the con-crete substrate is the only explanation for such an increase in

bond strength. Details of the process are not yet flilly under-stood.lt is evident that consistency in the delay period for meas-uring bond strength should be specifietl in quality-control procedures.

3.3 Freeze- Thaw Cycling

Many applications for metallized coatings on concrete in-volve exposure to freeze-thaw cycling, and thus its influence on the coating life cycle was determined. Bond strength measurc-mellls were made at regular intervals. No significant drop in the adhesion of the metallized coatings was observed afler 70 freeze-thaw cycles (Fig. 7),

4. Conclusions

Fig. 7 Bffect of fteele-thaw cycling on the adhesion to concrete of arc-sprayed zinc and 85Zn-15AI

o 20

Number of freeze-thaw cycles

60 60

•

Metallized

zinc

performs weB

as an

impressed-current

nn-ode.

• There is a loss of adhesion for metallized coalings with

higher current densities and longer polarization times.

Therefore, the zinc should be applied to the cOllerete sUth

that its adhesion is maximized and should not be used where excessively high current densities arc required. • Metallized 85Zn-15AI shoUld not be used as an

impressed-current anode due to poor bonding performance and an un-usual formation of largc air gaps underneath the disbanded coating.

• Zinc bond strength on concrete increases slightly during tlte tlrst few weeks after metallizing when no current is applied. • The adhesion of metaHized zinc on concrete does not

ap-pear to be influenced by severe freeze-thaw cycling.

Acknowledgments

The authors wish to thank the Intemational Lead Zinc Re-search Organization and the National ReRe-search Council of Can-ada for funding this research project. Special thanks to Dr. Serge Dallaire and Mr. Jean-Guy Allard from IMI(NRC) tor their as-sistance with the metallizing of the samples.

References

1. lA,Apostolos, D.M, Parks, and R,A, Carella, "Cathodic Protection Using Metallized Zinc: A 3.5 Years Progress Report," paper 131, pre· sented at Corrosion '87. National Association of Corrosion Engineers. 1987

2. I.A.Apostolos. D.M. Parks. and R.A. Carella. "Development, Testing

and Field Application of MetaIHzed Cathodic Protection Coatings on Reinforced Concrete Substructures," Stale ofCalifomia Department of Transport, Repon No.ｆｈｗａＯｃａｉｔｌｾＸＹＯＰＴＬ National Technicallnfor-mati on Service, Springfield. VA. 1989

52-Volume 5(1) March 1996

3. M,S. McGovern, CPOK with GnOT,Concrete Repair Dig.,OctINov t994.p29t·295

4. D.G. Manning and H.C. Schell, "Early Perfonnance of Eighl Experi-mental Cathodic Protection Systems at the Burlington Bay Skyway TestSite," Transportation ResearchRecord1041

5, E,W. Gulis and H. Jagasia, "Cathodic Protection 1993 Report:' Minis-try ofTransport of Ontario. StructuralOffice, ReportSO-94-0I 6. A.A, Sagues and R.O. Powers,"Low-Cost SprayedZinc Galvanic

An-ode for the Control of Corrosion of Reinforcing Steel in Marine Bridge Substructures," Strategic Highway Research Program. FinalReport, SHRP-88-tD024. 1994

7, R, Brousseau. M. Amott, S,Dallaire, andR.Feldman,Factors Af-fecting the Adhesion of Zinc on Concrete. Corrosion, Vol 48 (No.

Il),t992. P 947

8. R.Brousseau, M, Arnott,andS.Dallaire,"The Adhesion ofMetllllized Zinc Coatings on Concrete: Part1,"paper331,presented at Corrosion '93. NACE International, 1993

9. R Brousseau. M. Amott. and B. Baldock, "Improving the Adhesion of ZincCoatingsused to Metallize Concrete,"Maler. Perform.•lan1994,

p40

10, R.Brousseau,S.Dallaire, M. Arnott, B, Baldock. and lG, Allard. "The Adhesion of Thermally Sprayed Zinc on Reinforced Concrete," Final

ReportILZRO Z8-399, International Lead Zinc ResearchOrganization

11. R. Brousseau, M.Amott.andB.Baldock. "Arc Sprayed Zinc on Rein-forced Concrete," Final Report ILZRO ｚｅｾＳＹＰＬ Intcma!ional Lead ZincResearchOrganization

12. R. Brousseau, M. Amott. and B. Baldock. ·Laboratory Performance of Zinc Anodes for Impressed CUlTcnt Cathodic Protection of Reinforced Concrete, Corrosion. accepted for publication